This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Siderophores are bacterial products which bind iron and increase the rate of bacterial iron transport. Some iron-binding compounds are also known to function in media containing animal or human serum. Since iron sequestration is a known stimulus of bacterial growth during infections, siderophore synthesis has been linked to bacterial virulence. Pseudomonas aeruginosa produces two siderophores under iron-limiting conditions with different chelating properties, pyoverdine (PVD) and pyochelin (PCH). In order to elucidate the nature of the iron siderophore ligands in the two P. Aeruginosa siderophores, we are undertaking low temperature 9.5 GHz EPR studies which are particularly sensitive to the details of the iron ligand structure. This service project complements requests from other center users who wish to use center resources for studies of iron-protein interactions.